Cardiac pacing leads adapted for use in the coronary sinus have been available for quite some time, for example, the Medtronic Model No. 6992 coronary sinus lead was adapted for placement in the coronary sinus and could be employed to pace the left atrium or the left ventricle, depending upon the lead was advanced into the coronary sinus. Due to the difficulty of placement of the lead in the coronary sinus and the development of leads which provided for stable fixation in the atria and ventricles, left heart pacing via the cardiac venous system was not employed to any significant degree until relatively recently. Recently, there has been a renewed interest in left side pacing, particularly in the context of bi-ventricular pacing to treat heart failure. Recent coronary sinus pacing lead designs are disclosed in U.S. Pat. No. 5,935,160 issued to Auricchio et al, U.S. Pat. No. 5,931,864 issued to Chastain et al, U.S. Pat. No. 5,925,073, also issued to Chastain et al, U.S. Pat. No. 5,803,928 issued to Tockman et al, U.S. Pat. No. 5,755,766 issued to Chastain et al, U.S. Pat. No. 5,755,765 issued to Hyde et al, U.S. Pat. No. 5,466,254 issued to Helen, U.S. Pat. No. 5,800,495 issued to Machek et al, U.S. Pat. No. 5,476,498 issued to Ayers, and U.S. Pat. No. 5,433,729, issued to Adams.
As in the case of pacing of the right heart chambers, the ability to deliver a steroid or other anti-inflammatory drug is desirable in the context of left heart pacing. Patents disclosing electrodes adapted to deliver steroid include U.S. Pat. No. 4,711,251 issued to Stokes, U.S. Pat. No. 5,522,874 issued to Gates and U.S. Pat. No. 4,972,848 issued to Di Domenico et al., all incorporated herein by reference in their entireties. In most steroid eluding leads, the steroid is adapted to be dispensed adjacent that portion of the electrode which will be located in contact with heart tissue to be stimulated. In the context of leads located in the ventricles, this has typically resulted in a lead design in which a steroid is delivered through a distally facing port or ports, extending through the distal surface of the electrode. However, it is also known to deliver steroid by means of laterally directed ports, located proximal to the distal surface of the electrode, as disclosed in the above cited ""251 patent to Stokes and it is also known to deliver steroid by means of a ring shaped monolithic controlled release device located around the electrode, slightly proximal to its distal surface, as was employed in leads manufactured by Telectronics, Inc.
In the context of a lead to be implanted in the coronary vasculature, particularly after the lead has been advanced through the tortuous coronary venous system, it is often not clear which surface of the electrode which will actually be in contact with stimulatable tissue. This is particularly so in the context of a lead lacking any pre-formed bends intended to place a particular portion of the electrode in contact with stimulatable tissue. The present invention is directed toward improved drug eluting electrodes particularly adapted for use in the context of a coronary sinus lead, which are configured so that regardless of which portion of the electrode contacts stimulatable tissue, there will be an elution port for steroid or other anti-inflammatory agent located close by.
In both embodiments of the invention, the electrode includes a distal portion exposed to the exterior of the lead body and a shank extending proximal thereto, around which an MCRD containing a steroid or other anti-inflammatory drug is mounted. In one embodiment of the invention, the MCRD is coupled by means of internal channels within the electrode shank to a bore that extends to the distal surface of the electrode. In a second embodiment, the distal portion of the electrode is generally hemispherical and is provided with a shoulder that extends radially outward distal to the MCRD. The shoulder of the electrode is provided with distally directed bores extending from the distal surface of the MCRD to the surface of the distal portion of the electrode. In this second embodiment of the invention, the electrode shank includes a proximally directed internal lumen extending to the region of the shank around which the MCRD is mounted. This configuration allows for location of a stylet near the distal-most extremity of the lead, to assist in placement of the lead in a desired location in the coronary vascular system.